Answer:
d=126 (m)
Step-by-step explanation:
Let say:
d the distance from the bottom to the top
t1 the time used for running up
t2 the time for running down
[tex]\left\{\begin{array}{ccc}d&=&3*t_1\\d&=&7*t_2\\t_1+t_2&=&60\\\end{array}\right.\\\\\\\left\{\begin{array}{ccc}d&=&3*t_1\\t_2&=&\dfrac{3}{7} t_1\\t_1+\dfrac{3}{7} t_1&=&60\\\end{array}\right.\\\\\\\left\{\begin{array}{ccc}t_1&=&\dfrac{60*7}{10}=42 \\\\t_2&=&\dfrac{3*42}{7}=18\\\\d&=&3*42=126\\\end{array}\right.\\[/tex]
